We have a contamination or interference for the hydrolysate sample of hydroxyproline analysis. We think it is the product that we use that is the problem, because we can see a peak in the retention time of the hydroxyproline in a method blank. We have an 30-40 fold overestimation of our hydrolysate sample. We can see a shoulder peak or a split peak in those samples. Beside a contamination or interference problems coming from my product, do you have any other suggestion why I have a peak of hydroxyproline in a method blank?